Upgrades are suppose to be seamless, but there will always be a risk, however small.
If you have 14o4 LTS installed, then in theory you can go direct to 16o4 and skip the interm releases with a version upgrade.
http://www.googlubuntu.com/results/?cx=006238239194895611142:u-ocqbntw_o&q=version+upgrade&sa=Search&cof=FORID:9
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